1. Technical Field
The present invention relates to a projector and a control method thereof.
2. Related Art
In an ultrahigh-pressure mercury lamp (light source lamp) generally used as a light source of a projector, when the lamp temperature is too low, mercury is condensed, and problems of reduction in reliability, reduction in illuminance, and deterioration in hue arise. In the case where light control is performed by varying power of the light source lamp in response to a video signal (brightness level), temperature control of the lamp is important. It is necessary to secure the reliability, stabilize the illuminance, and maintain the hue while keeping the evaporated state of the mercury by holding the lamp temperature as high as possible. The temperature of the light source lamp may be appropriately adjusted by controlling the rotational speed of the cooling fan that blows air toward the lamp.
However, the cooling fan is also a source of noise and, if the rotational speed is frequently varied, the noise may be deteriorated. Accordingly, a method of controlling the rotational speed of the fan for a suitable temperature of the light source lamp based on an integral value (average value) of a brightness level of video signal or lamp power has been known (Patent Document 1 (Japanese Patent No. 4003796)). In Patent Document 1, a fan drive signal generation unit that controls the rotational speed of the fan based on an input signal from a lamp power level calculation unit and an input signal from a lamp drive level signal integration unit is provided.
The integral value of the brightness level of the video signal or lamp power is used so that the rotational speed of the fan may not be sensitive to the brightness level of the video signal. Thereby, the rotational speed of the fan smoothly varies and the rotational speed of the fan follows the variations of the brightness level of the video signal with a delay.
In the ultrahigh-pressure mercury lamp, when the brightness level of the video signal or the lamp power shifts from the lower state to the higher state, the lamp temperature rises and the mercury within the arc tube turns from the condensed state to the evaporated state. Further, the rotational speed of the cooling fan also shifts from the slower state to the faster state in response to the average value of the brightness level of the light source lamp. In this regard, to evaporate the mercury within the arc tube as fast as possible, the lamp temperature is desirably held as high as possible. Accordingly, when the brightness level of the video signal (lamp power) rises, the speed at which the rotational speed of the cooling fan increases is preferably lower, and the delay effect according to the method in related art may be exerted.
However, on the other hand, the following problem may occur. When the brightness level of the video signal or the lamp power shifts from the higher state (the higher state of the lamp power) to the lower state (the lower state of the lamp power), the mercury within the arc tube comes to be condensed. Concurrently, the rotational speed of the cooling fan shifts from the faster state to the slower state. It is desirable to keep the evaporated state of the mercury as far as possible, and thus, it is desirable to prevent cooling of the light source lamp by reducing the rotational speed of the cooling fan as fast as possible. However, in the method in related art, the speed at which the rotational speed of the cooling fan decreases is lower because of the above described delay effect, and cooling of the light source lamp is faster and the condensation of the mercury is accelerated.